A large number of beverages, to include a wide variety of food products, are packaged in plastic bottles and/or containers. Plastic has proven to be a useful material as it can be readily adapted and formed into a variety of shapes and sizes, as well as designs. Moreover, a variety of plastics can be used to form bottles to package beverages, for example, as well as containers for semi-solid food products to include mayonnaise and peanut butter. Such plastics include polyethylene, polyvinylchloride, and polyethylene terephthalate, also known as "PET" to those skilled in the industry.
The use of PET has grown due to the ease with which the material can be formed through a blow molding operation, either injection blow molding, stretch blow molding, or extrusion blow molding. Moreover, PET has the benefit of being lightweight, transparent, and has a superior resistance to impact, heat and pressure and lastly, it is 100% recyclable.
The shape, size and/or design of the molded PET container is a result of the design machined into a blow mold shell assembly. The shell assembly will typically include two opposed mold shell halves, each of which is machined, typically, from a ductile and durable metallic material, such as steel, to include stainless steel, and more recently aluminum. Aluminum offers the advantage of being lighter in weight, and easier to machine, although it can be more easily damaged. Once the mold shell halves are fabricated, they are then each affixed to a separate one of a pair of opposed support plates, also known as carrier plates or shell holders, which are themselves affixed to the blow mold machine, and more particularly to a shell opening and closing device.
In the blow mold process, a heated PET preform is positioned between the mold shell halves, whereupon the mold shell halves are then closed about the preform by the shell opening and closing device, at which point in time the preform is stretched, and compressed air or other suitable gases are passed into the preform such that it expands and takes on the shape of the mold cavity, and thus the container defined by the mold shell halves and an adjoining base portion of the mold which is moved into position as the shell halves close about the preform.
The known types of blow mold machines used for the process include linear or straight line blow mold machines which move the blow mold shells along a straight line toward and away from one another, as disclosed in U.S. Pat. Nos. 5,284,432 to Wurzer, and 5,551,861 to Baldi. The newer generation of blow molding machines are rotary blow mold machines, such as those shown in U.S. Pat. Nos. 3,854,855 to Pollock, et al.; 4,861,542 to Oles, etal.; 5,551,860 and 5,556,648, both to Budzynski, etal.; and 5,683,729 to Valles, which patent is assigned to Sidel S.A., the parent company of the assignee of this application.
In order to make a variety of containers in differing shapes, sizes and/or designs, it is necessary to "cut" molds for each such specific shape, size, and/or design. In order to produce a variety of shapes, sizes and designs among these blow mold containers, therefore, a container manufacturer or food packager can either have a machine dedicated to producing a certain type of container, or will be required to remove and replace differing blow mold shell sets, i.e. matching blow mold shell halves and the base assembly, from the blow mold machine when changing over from producing containers of a first size to a second size, for example. In a straight line blow mold machine such as that disclosed in the '861 patent to Baldi or the '432 patent to Wurzer, this is relatively easy to accomplish in that there typically is an adequate amount of room for a machine service technician to gain access to the molds, remove them from their carrier plates, and then install the new shell halves. However, on rotary blow mold machines, this becomes more of a problem.
U.S. Pat. No. 5,326,250 to Doudement, also assigned to the parent concern of the assignee of this invention, discloses an opening and closing mechanism for use in opening and closing a blow mold half shells on a rotary blow mold machine. As shown in Doudement, the mechanism is configured as a clam shell arrangement having a fixed pivot about which the mold shell halves will be pivoted for opening and closing. The carrier plates of the shell assembly will be affixed to the opening and closing mechanism, and in turn the blow mold shell halves will be removed from and replaced on their respective carrier plates based on the size, shape, or design of the container being produced.
The problem faced, however, by machine service technicians is that as this is a clam shell type of opening and closing mechanism, there is a limited amount of space available for gaining access to any threaded fasteners, or other fasteners which may be used for securing the blow mold shell halves to the holder or carrier plates. The changing over of the blow mold shell halves thus becomes a laborious and tedious process, made all the more difficult by the close confines within which these machines are typically housed. Thus, there is a need for an improved blow mold shell assembly in which the blow mold shells can be quickly and easily installed, removed, and replaced, as needed, to improve production efficiency and reduce the amount of machine downtime incurred when changing over the blow mold shell sets.
Another problem faced when changing over blow mold shell sets, more so on a clam shell type of holder arrangement on a rotary blow mold machine than with a straight line machine, is the alignment of the shell halves with their respective carrier plates. As known to those of skill in the art, a cooling or heat-treating fluid is oftentimes passed through conduits or channels defined in the carrier plate, the carrier plate in turn having ports which will be positioned in registry with inlet and discharge ports, respectively, defined in the blow mold shell halves. The precise alignment of the shell halves on the carrier plates is thus necessary in order to ensure that the cooling or heat-treating fluid does not leak out over the molds during the blow mold process, leading to undesirable or unacceptable containers, all of which tends to decrease machine efficiency. What is needed, therefore, is an improved blow mold shell assembly in which not only can the blow mold shells be quickly and easily removed and replaced, but which will also precisely align the blow mold shell with its respective carrier plate during the changeover process.
An additional problem faced by blow mold container manufacturers deals with the use of the newer generation of mold shell materials, for example aluminum. A great many blow mold shell halves are threadably affixed to their carrier plates by passing a threaded fastener through the carrier plate and into the mold shell, or by using clamps or straps which are threadably passed into both the carrier plate and the mold shell halve. The problem faced with using softer metals, for example aluminum, is that a machine service technician may over tighten a fastener such that the threads within the shell become stripped or destroyed, necessitating that the shell be removed from use and retapped, if possible, as the shell will no longer be securely fixed to its carrier plate, nor will it remain in a fixed position on its carrier plate during the high operating speeds employed by rotary blow mold machines. Moreover, due to the cost of machining blow mold shell halves, it is desirable that the service life of the shell half be extended for as long a time period as possible. What is needed, therefore, is an improved quick change blow mold shell assembly which will quickly and easily secure a blow mold shell half to its respective carrier plate without requiring the use of threaded fasteners passed into the blow mold shell.